1. Field of the Invention
Apparatus for treatment of stormwater runoff through volume-control-based detention and minimization of pollutant remobilization.
2. Description of the Related Art
This invention relates generally to liquid purification and separation and, more specifically, to an apparatus for separation of pollutants in urban stormwater runoff from the runoff water. This apparatus utilizes gravitational separation and tortuosity, resulting from a plurality of baffles both perpendicular to and oblique to the primary water flow direction, to trap substances less-dense and more-dense than water. This invention is differentiated from prior art by improved resistance to pollutant remobilization, resulting from an iterative experimental hydraulic design process. In addition, this invention provides a degree of retention through volume-control that exceeds that provided by existing gravitational, sub-surface, stormwater treatment systems.
Impacts of stormwater runoff on receiving environments have been documented extensively in engineering and scientific literature. Section 402 of the Federal Clean Water Act (CWA) regulates stormwater discharges through the National Pollutant Discharge Elimination System (NPDES). Treatment of stormnwater runoff using best management practices (BMPs) is a typical requirement of state and local regulations, as well. In the 1990s, there has been growing interest in xe2x80x98ultra-urban/space limitedxe2x80x99 BMP""s, such as sand filters, water quality inlets, and, reservoir/vault type of structures. Space constraints, high property values, soil conditions, and the proximity of other building foundations often preclude the use of conventional, space-intensive stormwater BMP""s such as detention ponds. For in-fill construction or redevelopment in built-up urban areas, where pollutant loads from urban runoff are usually the greatest, unconventional stormwater treatment technologies may be necessary.
Vault-type treatment technologies have been widely used for stormwater treatment in urban areas; however, the effectiveness of these devices for removal of suspended solids and oil and grease has been only marginal. A great weakness of these types of devices has been that large storm events tend to flush out the system, thereby releasing pollutants that were previously removed.
Prior art in the field of this invention of which the applicant is aware includes the following:
U.S. Pat. No. 4,127,488, Bell, J. A. et al., November 1978, Method and apparatus for separating solids from liquids.
U.S. Pat. No. 4,136,010, Pilie, R. J. et al., January 1979, Catch basin interceptor.
U.S. Pat. No. 4,328,101, Broden, C. V., May 1982, Device for separating particulate matter from a fluid.
U.S. Pat. No. 4,363,731, Filippi, R., December 1982, Device for regulating the flow of waste waters.
U.S. Pat. No. 4,383,922, Beard, H. J., May 1983, Waste water clarifier.
U.S. Pat. No. 4,983,295, Lamb, T. J. et al., Jan. 1991, Separator.
U.S. Pat. No. 4,985,148, Monteith, J. G., January 1991, Improved separator tank construction.
U.S. Pat. No. 5,004,534, Buzzelli, V., April 1991, Catch basin.
U.S. Pat. No. 5,186,821, Murphy, D. T., February 1993, Wastewater treatment process with cooperating velocity equalization, aeration, and decanting means.
U.S. Pat. No. 5,342,144, McCarthy, E. J., August 1994, Stormwater control system.
U.S. Pat. No. 5,520,825, Rice, W. M., May 1996, Oil-water separator.
U.S. Pat. No. 5,536,409, Dunkers, K. R., July 1996, Water treatment system.
U.S. Pat. No. 5,637,233, Earrusso, P. J., June 1997, Method and apparatus for separating grease from water.
U.S. Pat. No. 5,679,258, Petersen, R. N., October 1997, Mixed immiscible liquids collection, separation, and disposal method and system.
U.S. Pat. No. 5,759,415, Adams, T., June 1998, Method and apparatus for separating floating and non-floating particulate from rainwater drainage.
U.S. Pat. No. 5,788,848, Blanche, P. et al., August 1998, Apparatus and methods for separating solids from flowing liquids or gases.
U.S. Pat. No. RE30,793, Dunkers, K. R., November 1981, Apparatus for water treatment.
In addition to the patents listed above, a number of inventions in the general field of stormwater treatment methods and devices were discovered during the patent search. The inventions listed below have an element or elements similar to the invention disclosed herein; however, additional elements, details of elements, and/or applications of the inventions differ significantly from the forms and functions of the present invention. While the inventions listed below are intended to provide stormwater treatment, the principle of operation for many of these devices is filtration rather than sedimentation.
U.S. Pat. No. 4,298,471, Dunkers, K. R., November 1981, Apparatus for equalization of overflow water and urban runoff in receiving bodies of water.
U.S. Pat. No. 4,377,477, Dunkers, K. R., March 1983, Apparatus for equalization of overflow water and urban runoff in receiving bodies of water.
U.S. Pat. No. 4,664,795, Stegall, W. A. et al., May 1987, Two-stage waste water treatment system for single family residences and the like.
U.S. Pat. No. 4,747,962, Smissom, B., May 1988, Separation of components of a fluid mixture.
U.S. Pat. No. 4,865,751, Smissom, B., September 1989, Separation of components of a fluid mixture.
U.S. Pat. No. 5,080,137, Adams, T. R., January 1992, Vortex flow regulators for storm sewer catch basins.
U.S. Pat. No. 5,232,587, Hegemier, T. E. et al., August 1993, Stormwater inlet filters.
U.S. Pat. No. 5,322,629, Stewart, W.C., June 1994, Method and apparatus for treating stormwater.
U.S. Pat. No. 5,403,474, Emery, G. R., April 1995, Curb inlet gravel sediment filter.
U.S. Pat. No. 5,437,786, Horsley, S. W. et al., August 1995, Stormwater treatment system/apparatus.
U.S. Pat. No. 5,480,254, Autry, J. L. et al., January 1996, Storm drain box filter and method of use.
U.S. Pat. No. 5,549,817, Horsley, S. W. et al., August 1996, Stormwater treatment system/apparatus.
U.S. Pat. No. 5,702,593, Horsley, S. W. et al., December 1997, Stormwater treatment system/apparatus.
U.S. Pat. No. 5,707,527, Knutson, J. H. et al., January 1998, Apparatus and method for treating stormwater runoff.
U.S. Pat. No. 5,730,878, Rice, T., March 1998, Contaminated waste water treatment method and device.
U.S. Pat. No. 5,744,048, Stetler, C. C., April 1998, Clog resistant storm drain filter.
U.S. Pat. No. 5,770,057, Filion, G., June 1998, Overflow water screening apparatus.
U.S. Pat. No. 5,779,888, Bennett, P. J., July 1998, Filtering apparatus.
U.S. Pat. No. 5,810,510, Urriola, H., September 1998, Underground drainage system.
U.S. Pat. No. 5,840,180, Filion, G., November 1998, Water flow segregating unit with endless screw.
U.S. Pat. No. 5,890,838, Moore, Jr. Et al., April 1999, Stormwater dispensing system having multiple arches.
U.S. Pat. No. 5,972,216, Acemese, P. L. et al., October 1999, Portable multi-functional modular water filtration unit.
U.S. Pat. No. 5,985,157, Leckner, J. P. et al., November 1999, Filter device.
An aspect of this invention is to provide an apparatus for removal of pollutants with densities greater than and less than water from stormwater runoff.
Another aspect of this invention is to provide an apparatus that retains and immobilizes trapped pollutants, even during periods when flows are high.
Another aspect of this invention is to accumulate pollutants that are less and more dense than water until a time when the apparatus is cleaned out.
Another aspect of this invention is to minimize velocity in the vicinity of the bottom of the apparatus to minimize resuspension of deposited sediments and associated pollutants.
Another aspect of this invention is to provide an apparatus that can provide treatment of stormwater for larger tributary drainage areas by addition of modular sections.
Another aspect of this invention is to collect stormwater runoff and release it at a controlled rate over a specified period of time via an outflow opening.
Other aspects and advantages will become apparent hereinafter.
One aspect of the invention is a rectangular chamber of variable length and height assembled in a modular fashion. The rectangular chamber contains a system of overflow and underflow baffles, both perpendicular to and oblique to the primary direction of flow from the inlet to the chamber to the outlet from the chamber, which are located at opposite ends of the rectangular chamber. The baffles in the chamber serve several purposes including: flow momentum and energy dissipation, creation of a tortuous flow path, retention and immobilization of pollutants less and more dense than water, minimization of resuspension of sediments, and minimization of remobilization of floatable pollutants into the water column. The primary process for pollutant removal is gravitational separation, which occurs while water is detained in the chamber.
A baffle configuration for minimization of resuspension of trapped sediments and associated pollutants was first conceptualized by the inventors and then optimized by iterative experimentation involving three dimensional velocity measurements and dye visualization for a plurality of baffle configurations using a geometrically and hydraulically scaled physical model. Baffle configurations were evaluated for both dynamic (chamber filling and draining) and steady-state (chamber full with inflow rate equal to outflow rate) conditions. This exhaustive experimentation indicates that the baffle configuration of the invention disclosed minimizes resuspension of fine and coarse sediments and associated pollutants to a degree that exceeds the capabilities of prior art. In addition, a trapezoidal underflow baffle, the shape of which was optimized during hydraulic experimentation, impedes material less dense than water from entering the outflow section and exiting the vault. The trapezoidal configuration has the advantage of decreasing the downward velocity of water approaching and then moving under the baffle and into the outlet section and, thereby, decreases the risk of entraining floatable pollutants trapped behind the trapezoidal baffle into the flow passing into the outlet section.
In one aspect, the apparatus has an inlet that delivers water to the chamber from a tributary surface land area, either directly or via storm sewer system piping. Water entering the chamber passes through a system of underflow and overflow baffles both perpendicular to and oblique to the primary direction of flow from the inlet to the outlet, which is located at the end of the rectangular chamber opposite the inflow. As water enters the chamber, the water level in the chamber rises above the permanent pool water surface elevation, which normally is less than or equal to the elevation of the invert of the outflow opening. Outflow from the chamber is controlled by an opening that is sized to provide a specified time for the water in the chamber to drain from the elevation at which the chamber is full to the elevation of the permanent pool. When the rate of inflow is greater than the rate of outflow, the water level in the chamber will rise to the elevation at which the chamber is full. Once the chamber is full, any flow in excess of the outflow rate under full conditions will bypass the chamber via an overflow structure 294. When the rate of outflow is greater than the rate of inflow, the water surface elevation in the chamber will decrease at a rate controlled by the size of the outflow opening and the water surface elevation in the chamber to the elevation of the outflow opening invert, at which time outflow will cease.
Another aspect of the invention is a stormwater treatment apparatus, including a receptacle adapted to receive water flowing from a surface drainage area, the receptacle having a bottom and a top, the receptacle having an inlet and an outlet, the inlet and the outlet being in fluid communication with one another; and at least one baffle positioned within the receptacle between the inlet and the outlet, the baffle extending from the bottom of the receptacle, a first portion of the baffle and the bottom of the receptacle forming an angle therebetween.
A stormwater treatment apparatus varies from other types of treatment apparatus, such as septic tanks, in that stormwater treatment apparatus must capture a wide variety of particles of different sizes and compositions in a pulsed hydraulics environment, as opposed to the more constant flow environment of a septic tank. A stormwater treatment apparatus also differs from septic tanks in that the goal is to permanently trap sediments and other pollutants less or more dense than water, rather than to degrade organic matter and other biodegradable substances and in that a stormwater treatment apparatus is much larger than septic tanks, desirably having a volume of at least 500 cubic feet, more desirably at least 600 cubic feet and, preferably, at least 750 cubic feet.
The apparatus advantageously substantially reduces bottom velocities, thereby greatly reducing resuspension of sediments. In particular, the angle formed between the first portion of the baffle and the bottom of the receptacle is desirably between 30 and 60 degrees, at is desirably inclined in a downstream direction. Further, the height of the baffle is desirably at least two feet to limit the washing out of sediment. To facilitate manufacture and cleaning the baffle desirably includes a second portion, the second portion of the baffle extending from the bottom of the receptacle and forming an angle with the bottom of the receptacle, the angle being roughly 90 degrees.
The apparatus desirably includes an inlet baffle positioned between the inlet and the outlet, the inlet baffle spaced from said bottom and extending between generally opposing walls and an outlet baffle positioned between the inlet and the outlet, the outlet baffle spaced from said bottom and extending between generally opposing walls of the receptacle. The lower end of the outlet baffle is desirably positioned below said outlet. The outlet baffle advantageously may define a horizontal cross-section between a first baffle extending from said bottom and said outlet baffle larger than the horizontal cross-section between said first baffle and a vertical plane tangent to an upstream side of said outlet baffle. This has the effect of reducing the velocity of fluid. In this regard, it is desirable that outlet baffle defines a center section and at least one outer section which extends toward said outlet from said center section. Advantageously, however, the spaces between the outlet baffle and the opposing walls are sufficiently large to permit cleaning and to facilitate manufacture.
Yet another aspect of the invention is an apparatus for cleaning stormwater run-off, the apparatus including a vault having a top, a bottom, two sides, a front and a back, the vault comprising a first baffle extending from the bottom of the vault; a second baffle extending from the bottom of the vault, an inlet section having an opening and an outlet section having an outlet opening.